In general, when fuel is burned in an engine, nitrogen oxides are produced in exhaust gas. An EGR device recirculates the inactive exhaust gas and mixes it with intake air in a combustion chamber of the engine to decrease a combustion temperature, thereby suppressing the amount of product of nitrogen oxides. However, when the amount of exhaust gas is excessive, incomplete combustion is caused and hence the amount of recirculation of exhaust gas is controlled by an EGR valve.
However, the EGR valve is sometimes degraded by exhaust gas of high temperature. Further, since an EGR gas has high temperature and low absorption efficiency, it sometimes reduces an EGR effect. Then, in order to prevent these problems, a structure has been known in which an EGR cooler is mounted on an EGR pipe on the upstream side of the EGR valve. This kind of structure is disclosed in, for example, U.S. Pat. No. 6,213,105.
Embodiment 1 in the Prior Art
FIG. 1 is a perspective view to show the structure of an EGR device of embodiment 1 in the prior art which is disclosed in the above patent gazette. In the drawing, reference numeral 1 denotes an EGR valve. This EGR valve 1 is mainly configured of a housing 1a, a distribution chamber 1b formed in this housing 1a, a connection flange 1c that is formed on the housing 1a to connect the housing 1a to an exhaust pipe (not shown) for guiding exhaust gas which is discharged from the exhaust system of an engine (not shown), and a heat-intercepting flange 1d that is formed on the housing 1a and intercepts heat transfer between the housing 1a and adjusting means which will be described later. Adjusting means 2 for adjusting the opening of EGR valve 1 and an EGR cooler 3 for cooling the exhaust gas passing through the foregoing EGR valve 1 are connected to the housing 1a of EGR valve 1 via the heat-intercepting flange 1d. A connection plug 4 for supplying electric power is secured to an end portion of the adjusting means 2. The EGR cooler 3 is mainly configured of a bundle of cooling pipes (not shown) through which coolant such as cooling water for cooling the exhaust gas is flowed and a jacket 5 that surrounds the bundle of cooling pipes and flows the exhaust gas through space among the cooling pipes (not shown). A chamber 6 for supplying the coolant to the cooling pipes (not shown) is provided at one end of the EGR cooler 3 and a chamber 7 for recovering the coolant which is discharged from the cooling pipes (not shown) is provided at the other end. A connection part 8 to be connected to coolant supply means (not shown) is fixed to the bottom of chamber 6 and a connection part 9 to be connected to a coolant recovering part (not shown) is fixed to the top of chamber 7. An exhaust gas collecting chamber 10 for collecting the exhaust gas that passes through the EGR cooler 3 while being cooled is fixed to the chamber 7 and provided with a connection flange 11 for connecting exhaust gas collecting chamber 10 to an exhaust gas supply passage (not shown) for supplying the exhaust gas to the intake system of engine (not shown).
Next, an operation will be described.
The exhaust gas which is discharged from the exhaust system of engine (not shown) is supplied to the EGR valve 1 through an exhaust pipe (not shown) and the connection flange 1c from the direction shown by arrow A in the drawing. The opening of EGR valve 1 is adjusted by the adjusting means 2 according to a driving condition of the engine (not shown). When the EGR valve 1 is in a closed state, the exhaust gas is not supplied to the intake system of engine (not shown) and when the EGR valve 1 is in an open state, the exhaust gas is discharged from the distribution chamber 1b through the EGR cooler 3 to the direction shown by arrow B, whereby it is cooled to a predetermined temperature and returned to the intake system of engine (not shown). Here, the coolant flows into the EGR cooler 3 from the direction shown by arrow C and flows out in the direction shown by arrow D.
Embodiment 2 in the Prior Art
Moreover, in the EGR device, when the exhaust gas is cooled by the EGR cooler in cold weather, warming-up the engine (not shown) over a predetermined temperature is sometimes delayed to impair the functioning of a catalyst and the like. A technology disclosed, for example, in European Patent No. EP 1030050A1 is known as a structure to solve this problem.
FIG. 2 is a front view to show the structure of an EGR device of embodiment 2 in the prior art which is disclosed in the above European Patent gazette. In the drawing, reference numeral 20 denotes an EGR cooler. In the EGR cooler 20 is arranged a coolant pipe (not shown) for passing coolant such as cooling water. Then, a connection part 21 of the coolant pipe (not shown) can be connected to an external coolant supply pipe (not shown) and a connection part 22 can be connected to a coolant discharge pipe (not shown). A pipe 23 for passing the exhaust gas which is discharged from the exhaust system of engine (not shown) is arranged at an end portion on the upstream side of exhaust gas in the EGR cooler 20. Moreover, a bypass pipe 24 is arranged near the pipe 23 between an end portion of the upstream side of exhaust gas and an end portion of the downstream side of exhaust gas in the EGR cooler 20. An upstream opening end 24a of bypass pipe 24 and a downstream opening end 23a of pipe 23 function as valve seat which is provided at position where they can be alternately opened or closed when one valve body 25 is moved up and down. The valve body 25 is supported by a valve shaft 26 and the valve shaft 26 is slidably supported by a bearing 27 in the opening 20a of EGR cooler 20. The top end of valve shaft 26 is fixed to a diaphragm 28, and this diaphragm 28 and a case 29 form a closed space S. Moreover, a valve spring 30 for urging the valve body 25 which is fixed to the diaphragm 28 in the direction shown by arrow E is interposed between the diaphragm 28 and the case 29. Usually, in order to cool the exhaust gas of high temperature, the valve body 25 is pressed onto the upstream opening end 24a of bypass pipe 24 by the urging force of valve spring 30. Moreover, a connection part 29a for connecting the case 29 to external negative-pressure generating means (not shown) is fixed to the top of case 29.
Next, an operation will be described.
When the exhaust gas which is discharged from the exhaust system of engine (not shown) is higher than a predetermined temperature, the valve body 25 is pressed onto the upstream opening end 24a of bypass pipe 24 by the urging force of valve spring 30 to close the opening 24a and the exhaust gas is supplied through the downstream opening 23a of pipe 23 from the direction shown by arrow A in the drawing to an end portion 20b on the upstream side of exhaust gas in the EGR cooler 20. In the EGR cooler 20, the exhaust gas is cooled down to a predetermined temperature by coolant, then discharged from an end portion 20c on the downstream side of exhaust gas in the EGR cooler 20 along the direction shown by arrow B, and returned to the intake system of engine (not shown). On the other hand, when the exhaust gas is lower than the predetermined temperature, it does not need to be cooled. For this reason, pressure in the above-mentioned closed space S is reduced through the connection part 29a of case 29 by the external negative-pressure generating means (not shown), whereby the diaphragm 28 is deformed upward against the urging force of valve spring 30. At this time, when the diaphragm 28 is deformed, the valve shaft 26 is moved up to press the valve body 25 onto the downstream opening 23a of pipe 23, whereby the downstream opening 23a is closed. In this manner, the exhaust gas is passed through the end part 20b on the upstream side of exhaust gas in the EGR cooler 20 and the bypass pipe 24, discharged along the direction shown by arrow B from the end part 20c on the downstream side of exhaust gas in the EGR cooler 20, and returned to the intake system of engine (not shown)
However, in the EGR device of embodiment 1 in the prior art, as shown in FIG. 1, the adjusting means 2 and the EGR cooler 3 are so configured as to be connected to the EGR valve 1, so that it is impossible from a structural viewpoint to connect the bypass pipe 24 of embodiment 2 in the prior art to the EGR valve 1 and hence to return the exhaust gas to the intake system of engine (not shown) without cooling it in cold weather. Thus, there is presented a problem that this EGR device can not solve a trouble of delaying warming up and hence impairing the functioning of a catalyst and the like.
Further, the EGR device of embodiment 2 in the prior art, as shown in FIG. 2 is configured such that an exhaust gas passage is branched between the end portion 20b on the upstream side of exhaust gas and the end portion 20c on the downstream side of exhaust gas by the bypass pipe 24, so that the bypass pipe 24 is largely expanded outside from the EGR cooler 20. Thus, this presents a problem that this EGR device needs a large space for the bypass pipe 24 and hence cannot save space. Further, a need for separately providing the EGR valve increases the number of connection points and hence increases cost.
Still further, the EGR device of embodiment 2 in the prior art is configured such that the bypass pipe 24 is connected to the branching part of EGR cooler 20. Thus, this presents a problem that the branching part requires a welding work or the like and hence increases manufacturing cost.
Still further, the EGR device of embodiment 2 in the prior art is configured such that the bypass pipe 24 is connected to the branching part of EGR cooler 20. Thus, this produces a temperature difference between the EGR cooler 20 that is cooled and the bypass pipe 24 that is not cooled and hence a large difference in a change in length caused by thermal expansion between them. Therefore, there is presented a problem that stress is applied to the connection part between them and might break them.
The present invention has been made to solve the problems described above. It is the object of the present invention to provide an EGR device that might not be broken by a difference in thermal expansion, hence can be used for a long time, and is manufactured in a compact size and at low cost.